Browsing by Author "Liu, AY"

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An efficient load balancing strategy for scalable WAP gateways
(2005-06-02)
Lin, TH
;
Wang, KC
;
Liu, AY
;
資訊工程學系
;
Department of Computer Science
Clustering provides a promising way to build a scalable, reliable, and high-performance WAP gateway architecture. However, this requires an efficient load balancing mechanism for assigning a request to a suitable gateway in the cluster, that can offer the best service. In addition, unpredictable connection time and nonuniformity of incoming load from different mobile clients are big obstacles to load balancing among real gateways. In this paper, we propose a load balancing strategy that has the following features: (1) estimating the potential load of real gateways with small computation time and no communication overhead, (2) asynchronous alarm sent when the utilization of a real gateway exceeds a critical threshold, and (3) WAP-awareness. We also propose a scalable WAP gateway (SWG) architecture that consists of a WAP dispatcher and a cluster of real gateways. The WAP dispatcher is a front-end distributor with our load balancing strategy. To prevent the WAP dispatcher from becoming a bottleneck, the WAP dispatcher distributes mobile clients' requests in kernel space and does not process outgoing gateway-to-client responses. Experiment results show that our SWG has better load balancing performance, throughput, and delay compared to the LVS and the Kannel gateway. (C) 2004 Elsevier B.V. All rights reserved.
Enhancing Bluetooth performance in interference environments via channel-state-dependent packet scheduling with adaptive packet selection
(2004)
Shih, CH
;
Wang, KC
;
Liu, AY
;
資訊工程學系
;
Department of Computer Science
In this paper, we propose a Bluetooth channel state dependent data segmentation and reassembly (CSD-SAR) scheme and a queue state dependent priority (QSD-PR) scheduling policy. The CSD-SAR maintains a receiving frequency table to predict channel conditions and selects the best packet type and packet size to transmit data. In addition, the QSD-PR also uses the receiving frequency table to avoid bad frequencies and gives a selected master-slave pair, which has more queued data to send between each other and has a higher priority to eliminate the wastage of slots. The conventional scheduling policy, Round Robin (RR), yields poor performance with the time division duplex (TDD) based MAC protocol and results in slot wastage and may not ensure fairness. Simulation results show that our proposed scheme achieves better link utilization and higher throughput with bounded delay compared to the RR scheme in error-free and error-prone environments. Our scheme can also eliminate interference to other wireless networks that share the same spectrum, such as WLANs, by avoiding selecting channels occupied by other networks.